SET
CONSTRAINTS

Name

SET CONSTRAINTS -- set the constraint mode
of the current transaction

Synopsis

SET CONSTRAINTS { ALL | constraint [, ...] } { DEFERRED | IMMEDIATE }

Description

SET CONSTRAINTS sets the behavior of
constraint evaluation in the current transaction. In IMMEDIATE mode, constraints are checked at the
end of each statement. In DEFERRED
mode, constraints are not checked until transaction commit.

Note: This command only alters the behavior of
constraints within the current transaction. Thus, if you
execute this command outside of an explicit transaction block
(such as one started with BEGIN), it
will not appear to have any effect. If you wish to change the
behavior of a constraint without needing to issue a
SET CONSTRAINTS command in every
transaction, specify INITIALLY
DEFERRED or INITIALLY
IMMEDIATE when you create the constraint.

When you change the mode of a constraint to be IMMEDIATE , the new constraint mode takes effect
retroactively: any outstanding data modifications that would have
been checked at the end of the transaction (when using
DEFERRED) are instead checked during
the execution of the SET CONSTRAINTS
command.

Upon creation, a constraint is always give one of three
characteristics: INITIALLY DEFERRED,
INITIALLY IMMEDIATE DEFERRABLE, or
INITIALLY IMMEDIATE NOT DEFERRABLE.
The third class is not affected by the SET
CONSTRAINTS command.

Currently, only foreign key constraints are affected by this
setting. Check and unique constraints are always effectively
initially immediate not deferrable.

Compatibility

SQL92, SQL99

SET CONSTRAINTS is defined in
SQL92 and SQL99. The implementation in PostgreSQL complies with the behavior
defined in the standard, except for the PostgreSQL limitation that SET CONSTRAINTS cannot be applied to check or
unique constraints.

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